As is known in the art, heavy-duty or truck and bus (TBR) tires are formed with two annular bead portions, each having a metal bead bundle, and a layered cover turned up about the bead bundle. This layered cover typically includes a body ply, a reinforcing strip formed from an elastomeric material and an outer cover layer. The outer cover layer typically includes an innerliner formed of a material that is substantially impermeable to air, a sidewall and an abrasion gum strip connected to the innerliner by a splice. Tires with innerliner-abrasion gum strip splices are type-indicated IL-O-AGS (innerliner over abrasion gum strip).
In the tire industry, similar tires are produced which only differ from those described above by being AGS-O-IL types. That is, at each innerliner-abrasion gum strip splice, the axially inner lateral annular portion of the abrasion gum strip covers the lateral annular portion of the innerliner. More specifically, the innerliner of AGS-O-IL tires is normally extended laterally so that at each bead portion there is a lateral portion turned up about the bead bundle and interposed between the abrasion gum strip and reinforcing strip.
AGS-O-IL tires are undoubtedly more advantageous in terms of air sealing as the structure of the bead portions substantially prevent air from migrating slowly outwards through the carcass. It should be stated that with the exception of the innerliner, which is normally made from a substantially air impermeable mix such as bromobutyl, all the layers of elastomeric material used in the making of a tire are slightly permeable to air. In known AGS-O-IL tires of the type described i.e. having an innerliner with a lateral portion which is turned up at the bead portions and which is covered by the relative abrasion gum strip the danger of air filtering outwards close to the wheel rim, i.e. through the thickness of the abrasion gum strip not protected by the innerliner, still exists. Experience has shown however, that the air tends to migrate radially outwards through the abrasion gum strip and is immediately arrested by the turned-up portion of the innerliner.
Despite the above advantage, AGS-O-IL tires of the type described are substantially no longer used and have been replaced by corresponding IL-O-AGS tires of the type described above. The reason being that, given the considerable difference in hardness of the abrasion gum strip and innerliner materials, along with the poor “grip” of the innerliner to the surrounding layers, the axially inner part of each abrasion gum strip tends to work loose relatively quickly from the underlying innerliner. This can make the tire unsafe for remolding. This drawback is substantially eliminated in IL-O-AGS tires wherein the axially inner end of each abrasion gum strip is clamped by the innerliner.
In currently produced IL-O-AGS tires, each abrasion gum strip is mounted directly on the underlying reinforcing strip. Though this greatly improves the stability of the abrasion gum strips, such a method involves serious drawbacks with respect to air sealing, as the compressed air migrates through the carcass, and the ability of the tire to withstand on-rim assembly stress.
With respect to the effects of assembly stress on currently produced IL-O-AGS tires, tests have shown that the abrasion gum strips are unable at times to absorb assembly stress and are split locally by the wheel rim flanges. This is especially true when using automatic assembly fixtures because the abrasion gum strips are extremely hard and secured to the underlying reinforcing strips.